1. Field of the Invention
The present invention relates to a method for manufacturing a multi-layer printed circuit board for use in computers, VTR, portable telephones and the like. More particularly, the present invention relates to a method for manufacturing a build-up multi-layer printed circuit board in which an yttrium aluminum garnet (hereinafter, referred to as xe2x80x9cYAGxe2x80x9d) laser is used upon the formation of a via hole in the multi-layer printed circuit board, such that it can have the following advantages: the manufacturing process would become simple; the component packaging density and freedom for the design of the board would be improved; and a high speed of signal process would be ensured.
2. Description of the Prior Art
In the midst of the progress of the electronic components and the component installation technique, the printed circuit board was devised. Since that time, studies have been briskly carried out to make the printed circuit board highly dense. Particularly, the method for manufacturing the multi-layer printed circuit board by applying the build-up method is widely used. This method is different, from the general conventional method in which circuit layers having BVH(blind via holes) are formed, and this method is as follows. That is insulating layers and circuit conductive layers are alternately stacked to form a multi-layer printed circuit board. The manufacture of the printed circuit board based on the build-up method not only is simple, but also the formation of the via hole for serving as the connections between the different layers is easy. Further, in forming the via hole, extremely small diameters are possible, and the thickness of the circuit conductors is very thin, with the result that tiny circuits can be easily formed.
This build-up MLB(multi-layer board) is classified into two kinds in accordance with the method of forming the via hole. One is a method resorting to a chemical etching, and the other is a method using a laser. Recently, the method using a laser is widely used rather than the method resorting to the chemical etching. Further, in manufacturing the build-up MLB, generally the excimer laser is used.
FIG. 1 is illustrates the general process for manufacturing the build-up MLB by using the excimer laser.
As shown in FIGS. 1a and 1b, first an inner pattern 12 is formed by applying the general photo-etching process on a copper clad laminate(to be called xe2x80x9cCCLxe2x80x9d below) 10 having insulating layers(in th form of copper oxide) on th both faces thereof.
The CCL 10 with the inner pattern 12 formed thereon is pre-stacked on a copper foil 14 with an organic film 15 coated thereon. The pre-stacking is carried out by subjecting them to heating and pressing as shown in FIG. 1c. The organic film-coated copper foil 14 is the one on which an organic film 15 containing no inorganic fiber reinforcing agent such as polymide film is coated. However, in the case of the excimer laser, the processing of the copper is difficult, and therefore, in the pre-stacked board, the copper foil on the organic film-coated foil 14 has to be removed by etching before the hole is formed by means of the excimer laser. Or only the organic film 15 without the copper foil 14 may be used, but in this case, the pressing for the pre-stacking becomes difficult.
FIG. 1d illustrates a state in which the copper foil of the organic film-coated copper foil 14 has been removed.
Thereafter, as shown in FIG. 1e, the excimer laser beams are irradiated to the board to form a via hole 16. Under this condition, in the case of the build-up MLB, the via hole can be formed to a diameter of 0.05xcx9c0.2 mm.
Then as shown in FIG. 1f, the via hole 16 is electroplated by applying an electroless(chemical) copper plating to form an electroplated layer 17, so that the inner-layer contacts of the board can be efficiently realized. Then an electro plating is carried out to form a pattern 18 as shown in FIG. 1g. 
If the process steps of FIGS. 1c to 1g are repeated, the circuited layers can be stacked as much as desired.
Then finally, a through hole 19 is foamed by mechanical drilling or by using laser beams, thereby obtaining a build-up MLB as shown in FIG. 1h. 
The above described manufacturing process has to be carried out on the both faces of the substrate, but in the above, the descriptions were made only for one face for the sake of the describing simplicity.
In the above described conventional method, the via hole is formed by means of the excimer laser. In this case, the organic film-coated copper foil is completely removed by etching, and then, a Cu electroplating is carried out, this being a troublesome task. Particularly, during the use of the excimer laser, in order to prevent the scattering of the optical beams, an image hole mask has to be put on the organic film coated copper foil.
Further, in the case where a material RF-4 is used as substitution for the organic film, the use of the excimer laser becomes impossible. Therefore, the selection of the material for the insulating layer is limited, and the freedom for the drilling depth is lowered, with the result that the density is lowered, Besides, the excimer laser uses toxic gases such as Xe, Cl, XrF, and therefore, a perfect sealing is required. Therefore, the manufacturing factory may cause an environmental pollution.
An another example of methods for processing a via hole in a chemical etching manner is disclosed in U.S. Pat. No, 5,544,773.
In this conventional method, as shown in FIG. 1, a printed circuit pattern is formed on a copper clad laminate (CCL) having copper foils on the both faces thereof, and a resin coated copper foil (to be called xe2x80x9cRCCxe2x80x9d below) on the one face thereof is stacked on the CCL with the printed circuit pattern to form a pre-stacked board. Next, so as to form the via hole at a predetermined position on the pre-stacked board, first the copper foil on the RCC is primarily removed by using the chemical etching, and the remaining resin is melt by means of an alkali water solution. As mentioned, however, the conventional method should have a double process, which results in some problems in that the hole process is made in a complicated manner and thereby, the productivity would be decreased. Moreover, the hole process of a diameter of 100 xcexcm or less is not possible due to the resolution limit of an etch resist, such that a high integrated component packaging density would not be obtained. In addition, on the printed circuit board with one to three or more printed circuit layers formed thereon, the one to three or more printed circuit layers are not directly connected, such that the freedom for the design of the board would be lowered. On the other hand, in the conventional method the remaining resin within the bottom of the hole after completion of the hole process is removed by using a separate desmear process to ensure the reliability of electroplating within the via hole. At this time, in case of using KMnO4, the resins on the left and right portions within the interior of the via hole would be undesirably damaged.
As another example, there is the build-up MLB manufacturing technique of Japanese Patent Laid-open Hei-4-111497.
This build-up MLB manufacturing technique has the following features. That is, as shown in FIGS. 2a and 2b, a metal layer 22 is provided on one face, and as an intermediate layer, an insulating layer 20 or the insulating layer 20 plus a metal layer 23 and another insulating layer 25 are provided. On the other face, there is provided a metal layer(or a resist layer) 24. Then a via hole is formed by carrying out a wet etching or by means of laser beams.
That is, as shown in FIG. 2b, the metal layer or resist layer 24 is formed in the following manner. That is, the required area is removed as much as needed to expose the insulating layer 25, and then, the insulating layer 25 is removed by carrying out a wet etching. The above process steps are repeated as much as required to form a hole down to the metal layer 22. Then to the mental layer 22, laser beams are irradiated to remove(optically decompose) the etching residue and the insulating layer which is surface-coupled to the metal layer 22.
In the above method, the laser beams reach the bottom, and therefore, the inter-layer contacts are superior, thereby giving a high reliability.
However, in this method, in order to form the via hole, the conductive mental layer is partly exposed, and then, a wet etching and laser beams are used, with the result that the process is complicated.
As another example, there is the build-up MLB manufacturing technique of Japanese Patent Laid-open No. Hei-6-104568.
As shown in FIG. 3, an insulating film 35 is coated on a conductive supporting substrate 30 by pasting, and then, a material layer 33 highly sensitive to the laser beams is made to be stacked thereupon Then excimer laser beams are irradiated to form a hole 36 through the insulating film 35 and the material layer 33. Then on the material layer 33 which is highly sensitive to the laser beams, and around the hole 36, there is formed a printed pattern 38. Then an electroplating is carried out by utilizing the supporting substrate as a cathode.
In this method, the selection of the material for the insulating film is diversified, this being an advantage. However, the material layer which is highly sensitive to the laser beams is used for the laser drilling, and therefore, a superfluous process step is added.
The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore it is an object of the present invention to provide a method for manufacturing a build-up multi-layer printed circuit board in which a YAG(yttrium aluminum garnet) laser is used upon the formation of a via hole on a multi-layer printed circuit board, such that it can have the following advantages: the manufacturing process would become simple; the component packaging density and freedom for the design of the board would be improved; and a high speed of signal process would be ensured.
According to a first aspect of the present invention, there is provided a method for manufacturing a build-up multi-layer printed circuit board including the steps of: forming a first printed circuit pattern on a copper clad laminate (CCL) by applying a general photo-etching process, said CCL having a copper foil on the one face thereof; stacking a resin-coated (on one face) copper foil (RCC) on said CCL with said first printed circuit pattern formed thereon, and heating and pressing this structure; irradiating a YAG laser to the board with said RCC stacked so as to form a via hole at a predetermined position by removing said RCC; carrying out an electroless and electro copper plating on said board with via hole formed therein, to form a plated layer; and forming a second printed circuit pattern on said plated layer so as to electrically connect said first and second printed circuit patterns, wherein the thickness of the copper foil constituting said CCL is 3-35 xcexcm, the thickness of said RCC is 40-100 xcexcm, the process conditions of said YAG laser should satisfy the output power of preferably 300-2000 mW and the wavelength of preferably 200-1,500 nm, said via hole is formed in the diameter of 25-200 xcexcm and the depth of 20-100 xcexcm, and said electroplated layer is formed in thickness of 7-25 xcexcm.
According to a second aspect of the present invention, there is provided a method for manufacturing a build-up multi-layer printed circuit board including the steps of: forming a first printed circuit pattern on a copper clad laminate (CCL) by applying a general photo-etching process, said CCL having a copper foil on the one face thereof; primarily stacking a resin-coated (on one face) copper foil (RCC) on said CCL with said first printed circuit pattern formed thereon, and heating and pressing this structure; forming a second printed circuit pattern on the board with said RCC primarily stacked thereon by applying the general photo-etching process; secondarily stacking RCC on the board with said second printed circuit pattern formed thereon, and heating and pressing this structure; irradiating a YAG laser to the board with said RCC stacked secondarily so as to form a via hole at a predetermined position by removing said RCC stacked primarily and secondarily; carrying out an electroless and electro copper plating on the board with said via hole formed therein, to form a plated layer; and forming a third printed circuit pattern on said plated layer so as to electrically connect the layers on which said first to third printed circuit patterns are formed, wherein the thickness of the copper foil constituting said CCL is 3-35 xcexcm, the thickness of said RCC is at least 40-100 xcexcm, the process conditions of said YAG laser should satisfy the output of preferably 300-5000 mW and the wavelength of preferably 200-1,500 nm, said via hole is formed in the diameter of 25-200 xcexcm and the depth of 40-300 xcexcm, and said electroplated layer is formed in thickness of 7-25 xcexcm.
According to a third aspect of the present invention, there is provided a method for manufacturing a build-up multi-layer printed circuit board including the steps of: forming a first printed circuit pattern on a copper clad laminate (CCL) by applying a general photo-etching process respectively, said CCL having copper foils on both faces thereof; stacking a resin-coated (on one face) copper foil (RCC) on said CCL with said first printed circuit pattern formed thereon respectively, and heating and pressing this structure; irradiating a YAG laser to the board with said RCC stacked so as to form a via hole at a predetermined position by removing said RCC respectively; carrying out an electroless and electro copper plating on the board with said via holes formed therein, to form a plated layer; forming a second printed circuit pattern on said plated layer so as to electrically connect the layers on which said first and second printed circuit patterns are formed; and continuously stacking said RCC on the board formed according to said steps to form n printed circuit patterns, wherein the thickness of the copper foil constituting said CCL is 3-35 xcexcm, the thickness of said RCC is 40-100 xcexcm, the process conditions of said YAG laser should satisfy the output power of preferably 300-2000 mW and the wavelength of preferably 200-1,500 nm, said via hole is formed in the diameter of 25-200 m and the depth of 20-100 xcexcm, and said electroplated layer is formed in thickness of 7-25 xcexcm.
According to a fourth aspect of the present invention, there is provided a method for manufacturing a build-up multi-layer printed circuit board including the steps of: forming a first printed circuit pattern on a copper clad laminate (CCL) by applying a general photo-etching process respectively, said CCL having a copper foil on both faces thereof; primarily stacking a resin-coated (on one face) copper foil (RCC) on said CCL with said first printed circuit pattern formed thereon respectively, and heating and pressing this structure; forming a second printed circuit pattern on the board with said RCC primarily formed thereon by applying the general photo-etching process; secondarily stacking RCC on said second printed circuit pattern formed thereon respectively, and heating and pressing this structure; irradiating a YAG laser to the board so as to form a via hole at a predetermined position by removing said RCC stacked primarily and secondarily, carrying out an electroless and electro copper plating on the board with said via holes formed therein, to from a plated layer; forming a third printed circuit pattern on said plated layer so as to electrically connect the layers on which said first to third printed circuit patterns are formed; and continuously stacking said RCC on the board formed according to said steps to form n printed circuit patterns, wherein the thickness of the copper foil constituting said CCL is 3-35 xcexcm, the thickness of said RCC is at least 40-100 xcexcm, the process conditions of said YAG laser should satisfy the output of preferably 300-5000 mW and the wavelength of preferably 200-1,500 nm, said via hole is formed in the diameter of 25-200 xcexcm and the depth of 40-300 xcexcm, and said electroplated layer is formed in thickness of 7-25 xcexcm.
According to a fifth aspect of the present invention, there is provided a method for manufacturing a build-up multi-layer printed circuit board including the steps of: forming a first printed circuit pattern on a copper clad laminate (CCL) by applying a general photo-etching process respectively, said CCL having a copper foil on both faces thereof; primarily stacking a resin-coated (on one face) copper foil (RCC) on said CCL with said first printed circuit pattern formed thereon respectively, and heating and pressing this structure; irradiating a YAG laser to the board with said RCC stacked so as to form a plated through hole(PTH) at a predetermined position by removing said RCC stacked and said CCL; carrying out an electroless and electro copper plating on the board with said PTH formed therein, to form a plated layer respectively; forming a second printed circuit pattern on said plated layer to electrically connect the upper and lower portions of said second printed circuit pattern; secondarily stacking RCC on said second printed circuit pattern formed thereon respectively, and heating and pressing this structure; forming a third printed circuit pattern on the board with said RCC stacked secondarily thereon; and continuously stacking said RCC on the board formed according to said steps to form n printed circuit patterns, wherein the thickness of the copper foil constituting said CCL is 3-35 xcexcm, the thickness of said RCC is at least 40-100 xcexcm, the process conditions of said YAG laser should satisfy the output of preferably 300-5000 mW and the wavelength of preferably 200-1,500 nm, said PTH is formed in the diameter of 25-200 xcexcm and the depth of 400-800 xcexcm, and said electroplated layer is formed in thickness of 7-25 xcexcm.